Thin provisioning for ETERNUS DX/AF is based on:
Thin Provisioned Volumes (TPVs), i.e. volumes which, from the server's viewpoint, are configured with a capacity which is greater than their real available capacity
Thin Provisioned Pools (TPPs), i.e. predefined pools of physical disks for providing the physical storage space for Thin Provisioned Volumes
Thin Provisioned Volumes (TPVs)
TPVs are configured in the storage system with a particular physical size and labeled as TPVs. The size configured virtually for them can be considerably greater than the real size of a volume. The server sees the virtually configured size (capacity) of a volume and uses it like a conventional volume. In contrast to conventional volumes, the physical storage does not have to be fully assigned to the TPVs at configuration time. The physical storage place required for the TPVs is provided by a Thin Provisioned Pool.
Thin Provisioned Pools (TPPs)
TPPs arepools of one or more RAID groups (physical disks) to provide capacity for thin provisioning. The storage space for multiple TPVs is provided by one TPP.
A TPP always has one specified RAID type, but multiple RAID groups can be concatenated to form one TPP. Consequently a TPP can consist of multiple RAID groups of the same RAID type.
Different RAID types are implemented in different TPPs.
More than one TPP can be configured for each storage system. The maximum number depends on the model and is currently 256 TPPs for ETERNUS DX8700 S2.
The allocation unit in the TPP comprises 32 MB.
Monitoring the TPPs
Two threshold values are set on the storage system for each TPP to monitor the storage space consumption of the various TPPs. These are set when the TPPs are generated and can be modified during operation:
ATTENTION: 75% (default value) of the TPP's available capacity has been usedWARNING: 90% (default value) of the TPP's available capacity has been used
When the load on the TPP is 100%, writes to areas which have already been allocated are still executed, but writes which require a new area are rejected with an error.
SHC-OSD reports when each monitored TPP reaches the threshold values and also reports its current status. Monitoring by SHC-OSD can be set, see the THIN-POOL-MONITORING parameter in the SHC-OSD parameter file in the section "Configuration of SHC-OSD".
Configuration in the storage system
Thin provisioning is configured in the storage system by a qualified technician.
Proceed as follows:
Enter the license for the "Thin Provisioning Feature"
Generate TPPs from one or more RAID groups
Generate TPVs within a TPP
Set the monitoring threshold values for each TPP
Dynamic extension of the TPPs (when required)
When more storage is required for existing or future TPVs, existing TPPs can also be extended dynamically by additional physical devices. This extension takes place without interrupting any application which is executing.
Thin provisioning and replication functions
The following combinations of TPVs and replications are supported for ETERNUS DX/AF:
- QuickOPC: Replication from TPV to TPV
EC: Replication from TPV to TPV
REC: Replication from TPV to TPV
SnapOPC+: Replication from TPV to snap unit or TPV
In the case of EC and REC, TPVs and normal volumes can be combined. However, this is not recommended as the advantage of thin provisioning is then lost.
TPVs for the original and the mirror unit must reside in different TPPs.